The present invention relates generally to prime mover test systems and particularly to test systems which simulate vehicle driving schedules or cycles.
In recent years, the need has arisen to determine or measure the fuel economy, emissions, and durability of internal combustion engines used as prime movers for automobile vehicles. In many cases these tests are required in order to obtain federal government certification of the engines under Environmental Protection Agency (EPA) regulations. These tests are typically based upon standardized vehicle transient driving cycles, such as the EPA "Light Duty Urban Driving Cycle", the "Highway Fuel Economy Cycle" and the "Accelerated Mileage Accumulation Durability Driving Schedule."
Presently, three distinctly different testing methods or systems are used to perform the above identified engine tests. The most cumbersome and least repeatable of these test methods is test-track mileage accumulation. This method requires an entire vehicle to be driven around a course by a driver who attempts to repeatedly perform, with precision, a detailed set of test schedule instructions. Test track conditions are, of course, variable in nature, and vehicle mounting usually limits the sophistication and quantity of instrumentation available to record the necessary data. The second testing method employs a chassis dynamometer to simulate over-the-road vehicle environments. While testing on a chassis dynamometer offers improved reliability and repeatability with respect to the test-track method, an entire vehicle is required to occupy the test site. This not only consumes substantial laboratory space, but also leaves extraneous vehicle related variables and problems (such as tire noise and effects) in the engine testing equation. The third method employs a motor/generator electric dynamometer and a large-scale computer to test engines which have been removed from the vehicle. Although this method removes the extraneous variables contributed by the vehicle and driver and accurately produces road-load horsepower requirements, it is expensive and capital intensive. Furthermore, in order to simulate accelerated mileage accumulation (AMA), this system usually employs averaged data from the test track, which is the least repeatable method of all.
Accordingly, it is a principal object of the present invention to provide a novel prime mover testing system of simple and economical design which can accurately and repeatably simulate transient driving cycles in a laboratory environment.
It is a more specific object of the present invention to provide a transient driving cycle simulator test system which eliminates the need to base test schedules on track or chassis dynamometer speed and load data, and which removes the extraneous variables contributed by vehicles and drivers.
It is a further object of the present invention to provide a transient driving cycle simulator test system which is capable of simulating a plurality of vehicle driving schedules or cycles on the same test site.
It is an additional object of the present invention to provide a novel inertia wheel assembly for use in the transient driving cycle simulator test system which is capable of simulating vehicle acceleration and deceleration horsepower requirements.
In accordance with the foregoing objects, the present invention provides a transient driving cycle simulator test system for a prime mover, which generally comprises an inertia wheel means operatively coupled to the prime mover for simulating vehicle acceleration and deceleration horsepower requirements, a dynamometer means operatively coupled to the inertia wheel means for simulating vehicle road-load horsepower requirements, and microcomputer control circuit means for providing closed-loop control of the prime mover, the inertia wheel means and the dynamometer means in response to a set of predetermined transient driving cycle specifications. The inertia wheel means is calibrated to provide the equivalent inertia force of the vehicle being simulated, and features brake means for selectively retarding the rotation of an output shaft of the prime mover to provide forced deceleration of the vehicle being simulated. The dynamometer means is of the power absorption type capable of simulating the drivetrain, aerodynamic and rolling losses which define the vehicle road-load horsepower requirements.
The microcomputer control circuit means includes a microprocessor for providing a central processing unit, and an erasable programmable read-only memory (EPROM) for storing the set of predetermined transient driving cycle specifications and test sequence instructions. The control circuit means also includes transducer means for sensing at least the rotational speed of the output shaft of the prime mover, and the load applied by the dynamometer means. The control circuit means also includes input interface means for receiving signals from the transducer means and transmitting the signals to the microprocessor, and output interface means for transmitting control signals from the microprocessor to the prime mover, inertia wheel means and the dynamometer means. These control signals generally comprise a throttle signal for controlling the horsepower generated by the prime mover, a brake signal for selectively retarding the rotation of the output shaft of the prime mover and a load signal for controlling the resistance to rotation applied by the dynamometer means.
Additional advantages and features of the present invention will become apparent from a reading of the detailed description of the preferred embodiments which makes reference to the following sets of drawings in which: